Pre release changes (#6)

* Add Usage and Contributing guides

* Rename idx to index

* Filter primitives by type subtype and pattern

* Add more documentation.

* Remove MLPrimitives

* Fix filter

* Fix test

* Update subtype

* Update README

* Rename type and subtype to primitive_type and primitive_subtype

* Json keys

Author: pvk-developer

CONTRIBUTING.md

@@ -0,0 +1,99 @@
+# Contributing to SigPro
+
+Here you will find a series of steps that describe how to contribute a new implementation, fix or
+update to `SigPro` library.
+
+## 1. Clone the repository
+
+The first step would be to clone the `SigPro` repository. In order to do so
+make sure that you have access to the repository by accessing it direcly
+[https://github.com/signals-dev/SigPro/](
+https://github.com/signals-dev/SigPro/).
+
+If you have access to the repository and you have your `ssh` keys configured
+in your github account, you can clone it by using the following command
+
+```bash
+git clone [email protected]:signals-dev/SigPro.git
+```
+
+If you don't have your `ssh` keys configured you can clone the repository
+using your login name and password running the following command:
+
+```bash
+git clone https://github.com/signals-dev/SigPro
+```
+
+Next, you can enter your repository folder, create a virtualenv and install
+the project and the development dependencies.
+**Note**: You need to have virtualenv and virtualenvwrapper installed for
+these steps to work
+
+```bash
+cd SigPro
+mkvirtualenv sigpro
+make install-develop
+```
+
+## 2. Prepare your branch
+
+Before going any further, create the new `git` branch to which you will
+be pushing your development.
+
+To do so, type the following command with the desired name for your branch:
+
+```bash
+git checkout -b <name_of_your_branch>
+```
+
+Try to use the naming scheme of prefixing your branch with issue-X where X is
+the associated issue, such as issue-3-fix-foo-bug. And if you are not
+developing  on your own fork, further prefix the branch with your GitHub
+username, like githubusername/issue-3-fix-foo-bug.
+
+## 3. Code your changes
+
+Once you have your branch ready and set, you can start coding your changes.
+
+When doing so, ensure that the code is placed in its corresponding python
+file, and if you think that this doesn't exist, create it in the location
+that you find more suitable. However, when it comes to `aggregations` and
+`tranformations`, those are bound to their type and subtype.
+
+Also, while hacking your changes, make sure to follow the [PEP8](
+https://www.python.org/dev/peps/pep-0008/) style guide for python code
+and our `setup.cfg` (the main change is that we allow 99 characters per
+line).
+
+
+## 4. Test your changes
+
+Now that you have implemented your changes, make sure to  cover all your
+developments with the required unit tests, and that none of the old tests
+fail as consequence of your changes. For this, make sure to run the tests
+suite and check the code coverage by using the following commands:
+
+```bash
+$ make lint      # Check code styling
+$ make test      # Run the tests
+$ make coverage  # Get the coverage report
+```
+
+Once you have finished coding your changes, make sure to run the following
+command to ensure that your changes pass all the styling checks and tests
+including other Python supported versions using:
+
+```bash
+$ make test-all
+```
+
+## 5. Create a pull request
+
+Once you have created and tested your primitive, you can create a pull
+request by doing the following steps:
+
+0. (You did this previoulsy, but make sure) Create a new branch or ensure you are in the correct branch. Run the command `git branch` to see at which branch you are pointing. If you are in the desired follow the next step.
+1. Add the new files and the updated ones. By running `git status` you will see the modified and `new/untracked` files. Use `git add` to `add` the files that involve your implementation, such as the new primitive `json` file, the new module with the new transformation or aggregation and other changes that you may have done to existing files (such as `setup.py` if you updated or introduce a new dependency).
+2. Commit your changes using `git commit -m "Implement my new transformation"`.
+3. Push your branch: `git push --set-upstream origin <name_of_your_branch>`.
+4. Go to [https://github.com/signals-dev/SigPro/](https://github.com/signals-dev/SigPro/) and create a pull request from this branch to the master branch.